On 27 March 2013 16:59, Tom Taylor <[email protected]> wrote: > The meeting minutes record a disagreement over what port mapping algorithm > to use. This affects both MAP-E and LW 4over6. As I understand it: > > - either of these two technologies will work with either contiguous ports or > ports scattered according to the GMA algorithm > > - the real objection to GMA comes from Alain Durand, who wants to set up > simple min-port, max-port filters on his network equipment. > > > We all agree that port scattering offers negligible security advantage. > > The reason that I heard given for preferring GMA for MAP-E is that it > eliminates a restriction on the End-User Ipv6 address because the PSID is > free to range from 0 upwards rather than from some higher number upwards. I > don't follow this argument for two reasons: > > - you now have a restriction that the offset field A must range from 1 > upwards > > - the PSID field has an upper limit 2^k-1 imposed by the sharing ratio, > imposing a further restriction on the End-User IPv6 address value. > > Could someone spell out more clearly why the GMA was seen as necessary for > MAP-E?
GMA codifies (power of 2) logic that translates easily into hardware based longest match lookups. Furthermore, it is actually trivially simple to implement on any platform (not hardware restricted thus): Something like 2 lines of C code, in optimized form. Lastly, it is very efficient in terms of info encoding: a PSID conveys a code-point that maps the entire port space or port range. Finally, embedding a explicit port-range in an IPv6 address is not an option (the N:1 rule case). Regards, Woj. > _______________________________________________ > Softwires mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/softwires _______________________________________________ Softwires mailing list [email protected] https://www.ietf.org/mailman/listinfo/softwires
